A truncated HIV Tat demonstrates potent and specific latency reversal activity.

A major barrier to HIV-1 cure is caused by the pool of latently infected CD4 T-cells that persist under combination antiretroviral therapy (cART). This latent reservoir is capable of producing replication-competent infectious viruses once prolonged suppressive cART is withdrawn. Inducing the reactivation of HIV-1 gene expression in T-cells harboring a latent provirus in people living with HIV-1 under cART may result in depletion of this latent reservoir due to cytopathic effects or immune clearance. Studies have investigated molecules that reactivate HIV-1 gene expression, but to date, no latency reversal agent has been identified to eliminate latently infected cells harboring replication-competent HIV in cART-treated individuals. Stochastic fluctuations in HIV-1 tat gene expression have been described and hypothesized to allow the progression into proviral latency. We hypothesized that exposing latently infected CD4+ T-cells to Tat would result in effective latency reversal. Our results indicate the capacity of a truncated Tat protein and mRNA to reactivate HIV-1 in latently infected T-cells ex vivo to a similar degree as the protein kinase C agonist: phorbol 12-myristate 13-acetate, without T-cell activation or any significant transcriptome perturbation.

Long-term control of simian immunodeficiency virus (SIV) in cynomolgus macaques not associated with efficient SIV-specific CD8+ T-cell responses.

UNLABELLED: The spontaneous control of human and simian immunodeficiency viruses (HIV/SIV) is typically associated with specific major histocompatibility complex (MHC) class I alleles and efficient CD8(+) T-cell responses, but many controllers maintain viral control despite a nonprotective MHC background and weak CD8(+) T-cell responses. Therefore, the contribution of this response to maintaining long-term viral control remains unclear. To address this question, we transiently depleted CD8(+) T cells from five SIV-infected cynomolgus macaques with long-term viral control and weak CD8(+) T-cell responses. Among them, only one carried the protective MHC allele H6. After depletion, four of five controllers experienced a transient rebound of viremia. The return to undetectable viremia was accompanied by only modest expansion of SIV-specific CD8(+) T cells that lacked efficient SIV suppression capacity ex vivo. In contrast, the depletion was associated with homeostatic activation/expansion of CD4(+) T cells that correlated with viral rebound. In one macaque, viremia remained undetectable despite efficient CD8(+) cell depletion and inducible SIV replication from its CD4(+) T cells in vitro. Altogether, our results suggest that CD8(+) T cells are not unique contributors to the long-term maintenance of low viremia in this SIV controller model and that other mechanisms, such as weak viral reservoirs or control of activation, may be important players in control. IMPORTANCE: Spontaneous control of HIV-1 to undetectable levels is associated with efficient anti-HIV CD8(+) T-cell responses. However, in some cases, this response fades over time, although viral control is maintained, and many HIV controllers (weak responders) have very low frequencies of HIV-specific CD8(+) T cells. In these cases, the importance of CD8 T cells in the maintenance of HIV-1 control is questionable. We developed a nonhuman primate model of durable SIV control with an immune profile resembling that of weak responders. Transient depletion of CD8(+) cells induced a rise in the viral load. However, viremia was correlated with CD4(+) T-cell activation subsequent to CD8(+) cell depletion. Regain of viral control to predepletion levels was not associated with restoration of the anti-SIV capacities of CD8(+) T cells. Our results suggest that CD8(+) T cells may not be involved in maintenance of viral control in weak responders and highlight the fact that additional mechanisms should not be underestimated.

Restriction of HIV-1 replication in macrophages and CD4+ T cells from HIV controllers.

How HIV controllers (HICs) maintain undetectable viremia without therapy is unknown. The strong CD8(+) T-cell HIV suppressive capacity found in many, but not all, HICs may contribute to long-lasting viral control. However, other earlier defense mechanisms may be involved. Here, we examined intrinsic HIC cell resistance to HIV-1 infection. After in vitro challenge, monocyte-derived macrophages and anti-CD3-activated CD4(+) T cells from HICs showed low HIV-1 susceptibility. CD4 T-cell resistance was independent of HIV-1 coreceptors and affected also SIVmac infection. CD4(+) T cells from HICs expressed ex vivo higher levels of p21(Waf1/Cip1), which has been involved in the control of HIV-1 replication, than cells from control subjects. However, HIV restriction in anti-CD3-activated CD4(+) T cells and macrophages was not associated with p21 expression. Restriction inhibited accumulation of reverse transcripts, leading to reduction of HIV-1 integrated proviruses. The block could be overcome by high viral inocula, suggesting the action of a saturable mechanism. Importantly, cell-associated HIV-1 DNA load was extremely low in HICs and correlated with CD4(+) T-cell permissiveness to infection. These results point to a contribution of intrinsic cell resistance to the control of infection and the containment of viral reservoir in HICs.

Antibodies attenuate the capacity of dendritic cells to stimulate HIV-specific cytotoxic T lymphocytes.

BACKGROUND: Control of HIV is suggested to depend on potent effector functions of the virus-specific CD8(+) T-cell response. Antigen opsonization can modulate the capture of antigen, its presentation, and the priming of specific CD8(+) T-cell responses. OBJECTIVE: We have previously shown that opsonization of retroviruses acts as an endogenous adjuvant for dendritic cell (DC)-mediated induction of specific cytotoxic T lymphocytes (CTLs). However, in some HIV-positive subjects, high levels of antibodies and low levels of complement fragments coat the HIV surface. METHODS: Therefore we analyzed the effect of IgG opsonization on the antigen-presenting capacity of DCs by using CD8(+) T-cell proliferation assays after repeated prime boosting, by measuring the antiviral activity against HIV-infected autologous CD4(+) T cells, and by determining IFN-γ secretion from HIV-specific CTL clones. RESULTS: We find that DCs exposed to IgG-opsonized HIV significantly decreased the HIV-specific CD8(+) T-cell response compared with the earlier described efficient CD8(+) T-cell activation induced by DCs loaded with complement-opsonized HIV. DCs exposed to HIV bearing high surface IgG levels after incubation in plasma from HIV-infected subjects acted as weak stimulators for HIV-specific CTL clones. In contrast, HIV opsonized with plasma from patients exhibiting high complement and low IgG deposition on the viral surface favored significantly higher activation of HIV-specific CD8(+) T-cell clones. CONCLUSION: Our ex vivo and in vitro observations provide the first evidence that IgG opsonization of HIV is associated with a decreased CTL-stimulatory capacity of DCs.

Treatment interruption in chronically HIV-infected patients with an ultralow HIV reservoir.

OBJECTIVES: To investigate the potential for combination antiretroviral therapy (cART)-free remission following analytic treatment interruption (ATI) in chronically HIV-infected patients with ultralow cell-associated DNA. METHODS: Pilot study of patients (pts) with plasma viral load (pVL) less than 50 copies/ml for more than 2 years on cART, CD4 above 500 cells/µl, CD4/CD8 above 0.9, CD4 nadir above 300 cells/µl and HIV-DNA below 100 copies/10 peripheral blood mononuclear cells (PBMCs), undergoing treatment interruption. Ultrasensitive pVL, CD4 cell count, triplicate HIV-DNA were measured at D0, W2, W4, and every 4 weeks off-ART until W48 and at W4, W12 and W24 after ART resumption (RxR). RxR occurred in case of pVL rebound above 400 copies/ml or CD4 above 400 cells or HIV-related clinical event. The primary endpoint was the percentage of patients who did not reach RxR criteria at W24. Individuals were to be enrolled in three cohorts of five. Enrolment in cohort 2 began if at least one of five patients from cohort 1 remained in success at W8. Cohort 3 did not start. RESULTS: Ten patients were enrolled, with median (range) CD4 1118 cells/µl (608-1494), CD4/CD8 2.1 (1.4-2.6), HIV-DNA 66 copies/10 PBMC (<66-66) at screening, viral suppression of 4.9 years (2.9-8.3), CD4 nadir 495 cells/µl (330-739). One patient remained off-ART up to W48. Viral rebound occurred in nine of 10 patients at W2 (2 patients), W4 (6 patients) and W12 (one patient). pVL was resuppressed on cART at W4 (8 patients) and W12 (one patient). HIV DNA returned to baseline values within a median of 12 weeks following RxR. CONCLUSION: In a highly selected population of 10 patients with chronic HIV infection, an excellent immune status, durable virological suppression and ultralow reservoir, the success rate of ATI was 10% (95% confidence interval 0.3-44.5%) and nine of 10 patients had prompt rebound of plasma viremia. Resumption of ART led to return to baseline cell-associated total DNA.

Dendritic Cells from HIV Controllers Have Low Susceptibility to HIV-1 Infection In Vitro but High Capacity to Capture HIV-1 Particles.

HIV controllers (HICs), rare HIV-1 infected individuals able to control viral replication without antiretroviral therapy, are characterized by an efficient polyfunctional and cytolytic HIV-specific CD8+ T cell response. The mechanisms underlying the induction and maintenance of such response in many HICs despite controlled viremia are not clear. Dendritic cells play a crucial role in the generation and reactivation of T cell responses but scarce information is available on those cells in HICs. We found that monocyte derived dendritic cells (MDDCs) from HICs are less permissive to HIV-1 infection than cells from healthy donors. In contrast MDDCs from HICs are particularly efficient at capturing HIV-1 particles when compared to cells from healthy donors or HIV-1 patients with suppressed viral load on antiretroviral treatment. MDDCs from HICs expressed on their surface high levels of syndecan-3, DC-SIGN and MMR, which could cooperate to facilitate HIV-1 capture. The combination of low susceptibility to HIV-1 infection but enhanced capacity to capture particles might allow MDDCs from HICs to preserve their function from the deleterious effect of infection while facilitating induction of HIV-specific CD8+ T cells by cross-presentation in a context of low viremia.

Will it be possible to live without antiretroviral therapy?

PURPOSE OF REVIEW: Some individuals are able to control HIV infection (either viral replication or chronic immune activation) in the absence of therapy. We will consider recent insights into the mechanisms underlying control in these patients and how this has already encouraged the search for therapeutic approaches to induce a similar HIV functional cure in other patients. RECENT FINDINGS: Spontaneous reduction of HIV viremia to undetectable levels as observed in a few HIV-infected patients is associated with an efficient HIV-specific CD8 T-cell response, the characteristics of which are now better understood. However, maintenance of such control may involve alternative mechanisms. In particular, the presence of a very small viral reservoir seems necessary, although not sufficient, to ensure HIV control in the long term. Approaches designed to limit the early establishment of these reservoirs, to eliminate infected cells, or to avoid replenishment of the reservoirs have led to HIV remission in the absence of therapy in a few cases. Alternatively, other rare patients seem to deal with HIV infection by controlling immune activation despite high levels of viremia like the natural African monkey hosts do with SIV. These observations suggest that regulation of immune activation should be considered as a serious complement to conventional therapies targeting the virus itself. SUMMARY: A better understanding of the mechanisms underlying control of HIV infection or disease in some patients has already led to successful approaches in certain individuals. However, much work is still needed to generalize these results to the global population of HIV-infected patients.